The present invention relates to a composite tubular pipe structure intended to carry liquid or gaseous products, in particular for offshore petroleum production.
Composite tubes usually consist of parallel fiber layers such as glass fibers, carbon fibers, aramid fibers, embedded in a matrix. Each one of these layers has a given thickness and forms a given angle with the axis of the tube so as to meet criteria relative to the mechanical resistance to the stresses applied to the tube. The matrix can be a thermosetting matrix, an epoxy resin for example. However, the present invention is not limited to a thermosetting matrix, other materials can be used without departing from the scope of the present invention, thermoplastics for example.
Documents U.S. Pat. No. 5,110,644, U.S. Pat. No. 5,499,661, U.S. Pat. No. 5,091,230 describe composite tubes.
Such tubes can be used in particular in offshore oil prospecting and production operations, for example as risers connecting the sea bottom to the surface support for carrying the effluent produced. These composite tubes can notably advantageously replace, entirely or partially, rigid steel catenary risers, which are very heavy and subjected to stresses, notably bending stresses at the base, which can be very great and detrimental. A solution consists in using composite materials, much lighter, more flexible and fatigue resisting. The invention is not limited to these risers, it also relates to all the composite tubes having a sealing sheath that can be subjected to an external pressure.
In these types of tube, sealing against internal fluids is obviously fundamental, notably for the safety of the operations. It is however well-known that this type of composite is not considered to be sufficiently gas, water or hydrocarbon tight and at least one specific internal tube, referred to as liner, is required to provide sufficient sealing. This liner is generally made of organic materials, polymers of polyamide type or equivalent as regards sealing and implementation.
This polymer liner solution has the advantage of providing fluid tightness, good aging stability in a hydrocarbon environment, and it is compatible with the deformations of the composite, unlike a metal liner, for example in form of a continuous metal tube, cylindrical or corrugated. It however has several drawbacks, since it is notably difficult to obtain perfect and lasting sticking of the plastic layer to the upper composite layers made of fibers embedded in a matrix. Furthermore, gas permeation through the material of the inner liner, or permeation of sea water under pressure through the thickness of the composite layers is likely to produce a collapse pressure on this inner liner, which may eventually collapse.
The present invention thus relates to a multilayer tube comprising at least one layer of a composite material consisting of reinforcing fibers embedded in a matrix, at least one sealing sheath made of a polymer material intended to improve the tightness of this tube. The inner part of the tube consists of a metal carcass intended to protect the sheath against a possible external pressure.
According to the invention, the carcass is a flexible metal tube, for example made of a stapled steel tape or equivalent.
In a variant, the tube according to the invention comprises, on the outer surface thereof, a flexible metal tube, preferably made of stapled steel tape, intended to provide an external protection.
The tube according to the invention can comprise several sealing sheaths.
The present invention can be applied to constitute production risers of catenary or taut type, drilling risers, and even export lines connecting a production support and a loading buoy.